Electrical apparatus



NOV. 17, 1942. c, H, zlERDT, JR 2,302,086

ELECTRICAL APPARATUS Filed Aug. 12, 1941 Patentecl Nov. 17, 1942ELECTRICAL APPARATUS Conrad H. Zierdt, Jr., Pittsburgh, Pa., assignor toThe Union Switch and Signal Company, Swissvale, Pa, a corporation ofPennsylvama Application August 12, 1941, Serial No. 406,518

3 Ciaiins.

My invention relates to electrical apparatus, and it has particularreference to the provision of novel and improved means for shifting fromone element of an electrical circuit to a standby or alternate elementupon failure of the first element. More particularly, my inventionrelates to means for maintaining uninterrupted operation over a circuitincluding a plurality of circuit elements, and incorporating means forintroducing an alternate element into the circuit upon failure of one ofthe normally employed circuit elements.

In general, it is an object of my invention to provide novel andimproved means for auto matically replacing a circuit element, such as aballast lamp, resistor, signal indication lamp, or the like, by asimilar device upon failure of the first element.

Another object is the provision of novel and improved means forautomatically maintaining uninterrupted operation over a circuit upon afailure of an element of the circuit.

Other important objects and characteristic features of my invention willbe made clear as the specification progresses.

I shall describe one orm of apparatus embodying my invention, and shallthen point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic View illustrating a preferredform of apparatus embodying my invention.

Referring to the drawing, the reference character R designates a voltageresponsive relay connected in series with a current limiting device,such as a fuse F, and a load, designated by the reference character L,across a Voltage source which may, for example, comprise a directcurrent generator not shown but having its opposite terminals designatedby the referen e characters 13 and C. The reference characters EM andBLZ designate circuit elements, such as ballast lamps, resistors,incandescent signal indication lamps, or the like. For the purposes ofthe present description, it will be assumed that the devices BL areballast lamps of any suitable and well-known construction andcomprising, for example, a filament formed of a material, such as ironwire, mounted in a sealed envelope and having the characteristic ofchanging its resistance with changes in the voltage applied thereto.Each lamp BL may therefore be employed to cause the current flowing in acircuit in series with the filament to remain substantially constantthroughout a wide range of variations in the voltage impressed on thecircuit.

One lamp BLI or the other lamp BL2 is connected in multiple with relay Rand in series with load L across the source according as relay R isreleased or picked up to close its back contact l or its front contact2, respectively.

Relay R is selected and adjusted with respect to the constants of thecircuit elements BL, load L and the voltage of the source so as to beenergized at a value intermediate its release and its pick-up energylevels whenever current from the source is provided with multiple pathsincluding either element BL and the relay. Whenever, however, neitherelement BL is effective to provide a path for current in multiple withrelay R, as when the filament of lamp BLI fails or burns out, then relayR is picked up and closes its front contact I. Once relay R is picked updue to a failure of lamp BLI, the relay is energized above its releasedenergy level and accordingly remains in its picked-up position when theother lamp BLZ is connected over front contact 2 of the relay inmultiple with the relay Winding.

Normally, the apparatus is arranged so that relay R is released as shownin the drawing, and lamp BLI accordingly is connected in multiple withthe relay over its back contact I, whereby lamp BL! maintains asubstantially constant current flowing in the circuit including load L,and functions to limit the voltage impressed across relay R to a valueinsufficient to enable the relay to pick up. In the event, however, of afailure of the lamp filament, device BL! is no longer effective to limitthe voltage applied to relay R, whereupon approximately the full voltageof the source is applied to the relay to cause the relay to pick up andclose its front contact 2 to connect the alternate 0r stand-by deviceBL2 across the load in multiple with the relay winding. Lamp BLZ becomeseffective to limit the voltage applied to the relay, and thus causes theenergy level in the relay to decrease to a value above its drop-awayvalue, whereupon relay R retains its front contact 2 closed to maintainlamp BLZ connected in multiple therewith. It is apparent that apparatusembodying my invention provides means eifective in the event of afailure of a circuit element normally connected in circuit with thevoltage source to replace such element by a stand-by or alternatecircuit element. It follows, therefore, that such apparatus providesmeans for maintaining uninterrupted operation over a circuit uponfailure of a circuit element.

The current limiting device or fuse F is provided to preclude thepossibility of improper operation of the circuit in the event of acomplete or partial short-circuit of the coil of relay R. Should thecoil of relay R become short-circuited, the current through fuse F willof course increase, and by properly proportioning the fuse, it isapparent that the fuse may be adjusted to fail when the current throughthe coil of relay R increases abnormally due to a complete or partialshort-circuit of the relay coil.

Although I have herein shown and described only one form of apparatusembodying my invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a voltage source, a voltage responsive relay havingits winding connected in series with said source, and two lamps one orthe other connected to said source in multiple with said relay windingaccording as the armature of said relay is released or picked uprespectively, the armature of said relay normally being released andsaid rela winding having a resistance selected with respect to theresistances of said lamps and the voltage of said source, to beefiective when either lamp is energized in multiple with the reiaywinding to limit the current in the winding to a value below the pick-upbut above the release value of the relay and eiiective when neither lampis energized in multi ple with the relay winding to permit the currentin the winding to reach the pick-up value of the relay, whereby saidrelay normally maintains its armature released to cause said one lamp tobe energized in multiple therewith until the filament of such lamp failsor burns out whereupon said relay armature is picked up to connect saidother lamp to said source in multiple with said relay winding.

2. In combination, a voltage source, a voltage responsive relay havingits winding connected to said source, two circuit elements, a circuitincluding a back contact of said relay for connecting one of saidcircuit elements to said source in multiple with said relay winding, andanother circuit including a front contact of said relay for connectingthe other of said circuit elements to said source in multiple with saidrelay winding, the armature of said relay normally being releasedwhereby said back contact is normally closed, and said relay windinghaving a resistance preselected with respect to the constants of saidcircuit elements and. the voltage of such source, to be effective wheneither circuit element is energized in multiple with the relay windingto limit the current in such winding to a value below the pick-up butabove the release value of the relay and efiective whenever neithercircuit element is energized in multiple with the relay winding topermit the ciu-rent in such winding to reach the pick-up value of therelay, whereby said relay normally maintains its back contact closed tocause said one circuit element to be energized until such element failswhereupon said relay closes its front contact and maintains such contactclosed to cause said other circuit element to be energized.

3. In combination, a source of current, a load, a voltage responsiverelay, a circuit connecting said load and the winding of said relay inseries with said source, and two resistors one connectahis in saidcircuit in multiple with said relay winding over a back contact of saidrelay and the other connectable in said circuit in multiple with saidrelay winding over a front contact of said relay, said relay normallybeing released and said relay winding having a resistance preselectedwith respect to the voltage of said source and to the values of saidresistors, to limit the current in said relay winding to a value belowits pick-up but above its release value whenever either resistor isenergized in multiple with said winding but permitting the current insaid relay winding to reach its pick-up value whenever neither resistoris energized in multiple with said winding, whereby said relay normallymaintains its back contact closed to eifect energization of said oneresistor until such resistor fails and then said relay picks up andmaintains its front contact closed to effect energization of said otherresistor.

CONRAD H. ZIERDT, JR.

